The problem of an objective identification of defects supporting Partial Discharges (PD) in different types of insulation systems adopted in ac rotating machines, is approached. The solution proposed here relies on a set of robust identification markers capable of describing the shape of the PD patterns resorting to a tree structure according to the symmetry/asymmetry of PD in voltage phase and polarity. A fuzzy tree structure is used to reflect the inherent uncertainty of source identification based on the shape analysis in the identification results. PD occurring in the same defective component used in different insulation technologies (e.g., Resin-Rich or VPI technology, taped or varnished stress-grading system), can generate different PD patterns. Thus, different tree-structures, each one pertinent to an insulation technology, have been developed to achieve a more accurate defect identification even if the problem of ambiguous PD patterns requires additional investigations.
